Mercury in the Guadalupe Watershed

Between 1850 and 1920, it’s estimated that 6,500 tons of mercury, the most toxic of all natural metals, seeped into the local streams. The most dangerous form of mercury is Methylmercury and it’s this form that is of biggest concern to the Santa Clara Valley Water District. It’s also one of the area’s biggest sources of mercury contamination, the legacy of mining work during the California Gold Rush in the 1800s.

The Guadalupe River Watershed is 170-square miles of six reservoirs and more than 80 miles of streams.

Eating contaminated fish and other organisms at the top of the aquatic food chain is the most common way that people become exposed to Methylmercury. It can cause problems with the immune system and damage a person’s nervous system, creating issues with coordination and the senses of touch, taste and sight. Because it’s readily absorbed when ingested and excreted very slowly, most of it stays in person’s system. Pregnant women and young children are the most susceptible to mercury poisoning.

The water district has intensely monitored the mercury situation – given that less than a teaspoon of methylmercury can poison thousands of fish – with the goal to remove the mercury before it hits the water and affects people and wildlife.

Since 2007, the agency has undertaken six projects to remove the mercury. The work will take place over 20 years, with recovery projected in about 120 years. If that sounds like a long time, remember the majority of mercury is the legacy of mining dating back 150 years. As the amount of mercury in sediment decreases, concentrations in fish will also decline, reducing risk to people and wildlife.

Learn more by clicking on the "Mercury Contamination" links at left, or click on the project name in the map below.